Techopedia explains 1000BASE-X

1000BASE-X consists of various standards. These include:

1000BASE-CX (Copper)

1000BASE-KX

1000BASE-SX

1000BASE-LX (both for single- and multi-mode fiber)

1000BASE-LX10

1000BASE-EX

1000BASE-ZX

1000BASE-BX10

The range of 1000BASE-X starts at 25 meters for copper and can be extended to 70 km with a single-mode fiber channel. All of these standards use an 8b/10b encoding scheme, in which 8 bits are used for data transmission and 2 for error correction.